(i) Technical Field
The present invention relates to a system to control a wavelength and a method to control a wavelength.
(ii) Related Art
Japanese Patent Application Publication No. 2001-308444 (hereinafter referred to as Document 1) discloses a technology in which a first photodiode to monitor a light transmitting an optical filter having a periodic function of a wavelength and a second photodiode to monitor whole optical power of an incident light into the optical filter are provided, and a wavelength is monitored with use of outputs of the two photodiodes.
And, Japanese Patent Application Publications No. 2002-196131 (hereinafter referred to as Document 2) and No. 2002-202190 (hereinafter referred to as Document 3) disclose a technology in which a wavelength is monitored with use of outputs of two photodiodes that monitors two optical beam transmitting an optical filter achieving two characteristics of optical transmission characteristics in which an amplitude period is relatively shifted from a single etalon filter by π/2.